Integrated Services Digital Network

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ISDN telephone ISDN telefono.jpg
ISDN telephone

Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. Work on the standard began in 1980 at Bell Labs and was formally standarized in 1988 in the CCITT "Red Book". [1] By the time the standard was released, newer networking system with much greater speeds were available, and ISDN saw relatively little uptake in the wider market. One estimate suggests ISDN use peaked at a worldwide total of 25 million subscribers at a time when 1.3 billion analog lines were in use. [2] ISDN has largely been replaced with digital subscriber line (DSL) systems of much higher performance.

Contents

Prior to ISDN, the telephone system consisted of digital links like T1/E1 on the long-distance lines between telephone company offices and analog signals on copper telephone wires to the customers, the "last mile". At the time, the network was viewed as a way to transport voice, with some special services available for data using additional equipment like modems or by providing a T1 on the customer's location. What became ISDN started as an effort to digitize the last mile, originally under the name "Public Switched Digital Capacity" (PSDC). [2] This would allow call routing to be completed in an all-digital system, while also offering a separate data line. The Basic Rate Interface, or BRI, is the standard last-mile connection in the ISDN system, offering two 64 kbps "bearer" lines and a single 16 kbps "delta" channel for commands and data.

Although ISDN found a number of niche roles and some wider uptake in specific locales, the system was largely ignored and garnered the industry nickname "innovation subscribers didn't need." [3] It found a use for a time for small-office digital connection, using the voice lines for data at 64 kbps, sometimes "bonded" to 128 kbps, but the introduction of 56 kbps modems undercut its value in many roles. It also found use in videoconference systems, where the direct end-to-end connection was desirable. The H.320 standard was designed around its 64 kbps data rate. The underlying ISDN concepts found wider use as a replacement for the T1/E1 lines it was originally intended to extend, roughly doubling the performance of those lines.

History

Digital lines

Since its introduction in 1881, the twisted pair copper line has been installed for telephone use worldwide, with well over a billion individual connections installed by the year 2000. Over the first half of the 20th century, the connection of these lines to form calls was increasingly automated, culminating in the crossbar switches that had largely replaced earlier concepts by the 1950s. [2]

As telephone use surged in the post-WWII era, the problem of connecting the massive number of lines became an area of significant study. Bell Labs seminal work on digital encoding of voice led to the use of 64 kbps as a standard for voice lines (or 56 kbps in some systems). In 1962, Robert Aaron of Bell introduced the T1 system, which allowed a pair of twisted pair lines to carry 1.544 Mbps of data over a distance of about one mile. This was used in the Bell network to carry traffic between local switch offices, with 24 voice lines and a separate 8 kbps line for signaling commands like connecting or hanging up a call. This could be extended over long distances using repeaters in the lines. T1 used a very simple encoding scheme, alternate mark inversion (AMI), which reached only a few percent of the theoretical capacity of the line but was appropriate for 1960s electronics. [3]

By the late 1970s, T1 lines and their faster counterparts, along with all-digital switching systems had replaced the earlier analog systems for most of the western world, leaving only the customer's equipment and their local end office using analog systems. Digitizing this "last mile" was increasingly seen as the next problem that needed to be solved. However, these connections now represented over 99% of the total telephony network, as the upstream links had increasingly been aggregated into a smaller number of much higher performance systems, especially after the introduction of fiber optic lines. If the system was to become all-digital, a new standard would be needed that was appropriate for these lines, which might be miles long and of widely varying quality. [3]

ISDN standarization

Around 1978, Ralph Wyndrum, Barry Bossick and Joe Lechleider of Bell Labs began one such effort to develop a last-mile solution. They studied a number of derivatives of the T1's AMI concept and concluded that a customer-side line could reliably carry about 160 kbps of data over a distance of 4 to 5 miles (6.4 to 8.0 km). That would be enough to carry two voice-quality lines at 64 kbps as well as a separate 16 kbps line for data. At the time, modems were just starting to push into the 1200 bps range, and the 2400 bps standard would not be completed until 1984, so the 16 kbps represented a significant advance in performance in addition to being a separate channel and thus allowing voice and data at the same time. [3]

A key problem was that the customer might only have a single twisted pair line to the location of the handset, so the solution used in T1 with separate upstream and downstream connections was not universally available. With analog connections, the solution was to use echo cancellation, but at the much higher bandwidth of the new concept, this would not be so simple. A debate broke out between teams worldwide about the best solution to this problem; some promoted newer versions of echo cancellation, while others preferred the "ping pong" concept where the direction of data would rapidly switch the line from send to receive at such a high rate it would not be noticeable to the user. John Cioffi had recently demonstrated echo cancellation would work at these speeds, and further suggested that they should consider moving directly to 1.5 Mbsp performance using this system. The suggestion was laughed off the table, [lower-alpha 1] but the echo cancellation concept was taken up by Joe Lechleider eventually came to win the debate. [3]

Meanwhile, the debate over the enoding scheme itself was also ongoing. As the new standard was to be international, this was even more contentious as several regional digital standards had emerged in the 1960s and 70s and merging these back together was not going to be easy. To further confuse issues, in 1984 the Bell System was broken up and the US center for development moved to the American National Standards Institute (ANSI) T1D1.3 committee. Thomas Starr of the newly-formed Ameritech led this effort and eventually convinced the ANSI group to select the 2B1Q standard proposed by Peter Adams of British Telecom. This standard used a 80 kHz base frequency and encoded two bits per baud to produce the 160 kbps base rate. Ultimately Japan selected a different standard, and Germany selected one with three levels instead of four, but all of these could interchange with the ANSI standard. [4]

Rollout

With ISDN allowing digital-quality voice, two separate lines and all-the-time data, the telephony world was convinced there would be high customer demand for such systems. This proved not to be the case. During the lengthy standardization process, new concepts, especially local area networks like Ethernet, provided performance around 10 Mbps which had become the baseline for computer connections. Additionally, modems had continued improving, introducing 9600 bps systems in the late 1980s and 14.4 kbps in 1991, significantly eroded ISDN's value proposition for the average customer. [4]

Meanwhile, Lechleider had proposed using ISDN's echo cancellation and 2B1Q encoding on existing T1 connections, doubling the distance between repeaters to about 2 miles (3.2 km). Another standards war broke out, but in 1991 Lechleider's 1.6 Mbps "High-Speed Digital Subscriber Line" eventually won this process as well after Starr drove it through the ANSI T1E1.4 group. A similar standard emerged in Europe to replace their E1 lines, increasing the sampling range from 80 to 100 kHz to allow 2.048 Mbps. [5] By the mid-1990s, these Primary Rate Interface (PRI) lines had largely replaced T1 and E1 between telephone company offices.

ISDN becomes ADSL

Lechleider also believed this higher-speed standard would be much more attractive to customers than ISDN had proven. Unfortunately, at these speeds, the systems suffered from a type of crosstalk known as "NEXT", for near-end crosstalk. This made longer connections on customer lines difficult. Lechleider noted that NEXT only occurred when similar frequencies were being used, and could be diminished if one of the directions used a different carrier rate, but doing so would reduce the potential bandwidth of that channel. Lechleider suggested that most consumer use would be asymmetric anyway, and that providing a high-speed channel towards the user and a lower speed return would be suitable for many uses. [5]

This work in the early 1990s eventually led to the ADSL concept, which emerged in 1995. An early supporter of the concept was Alcatel, who jumped on ADSL while many other companies were still devoted to ISDN. Krish Prabu stated that "Alcatel will have to invest one billion dollars in ADSL before it makes a profit, but it is worth it." They introduced the first DSL Access Multiplexers (DSLAM), the large multi-modem systems used at the telephony offices, and later introduced customer ADSL modems under the Thomson brand. Alcatel remained the primary vendor of ADSL systems for well over a decade. [6]

ADSL quickly replaced ISDN as the customer-facing solution for last-mile connectivity. ISDN has largely disappeared on the customer side, remaining in use only in niche roles like dedicated teleconferencing systems and similar legacy systems.

ISDN elements

Integrated services refers to ISDN's ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of what were expected to be most people's complete communications needs (apart from broadband Internet access and entertainment television) at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. It also refers to integrated switching and transmission [7] in that telephone switching and carrier wave transmission are integrated rather than separate as in earlier technology.

Basic Rate Interface

The entry level interface to ISDN is the Basic Rate Interface (BRI), a 128 kbit/s service delivered over a pair of standard telephone copper wires. [8] The 144 kbit/s overall payload rate is divided into two 64 kbit/s bearer channels ('B' channels) and one 16 kbit/s signaling channel ('D' channel or data channel). This is sometimes referred to as 2B+D. [9]

The interface specifies the following network interfaces:

BRI-ISDN is very popular in Europe but is much less common in North America. It is also common in Japan — where it is known as INS64. [10] [11]

Primary Rate Interface

The other ISDN access available is the Primary Rate Interface (PRI), which is carried over T-carrier (T1) with 24 time slots (channels) in North America, and over E-carrier (E1) with 32 channels in most other countries. Each channel provides transmission at a 64 kbit/s data rate.

With the E1 carrier, the available channels are divided into 30 bearer (B) channels, one data (D) channel, and one timing and alarm channel. This scheme is often referred to as 30B+2D. [12]

In North America, PRI service is delivered via T1 carriers with only one data channel, often referred to as 23B+D, and a total data rate of 1544 kbit/s. Non-Facility Associated Signalling (NFAS) allows two or more PRI circuits to be controlled by a single D channel, which is sometimes called 23B+D + n*24B. D-channel backup allows for a second D channel in case the primary fails. NFAS is commonly used on a Digital Signal 3 (DS3/T3).

PRI-ISDN is popular throughout the world, especially for connecting private branch exchanges to the public switched telephone network (PSTN).

Even though many network professionals use the term ISDN to refer to the lower-bandwidth BRI circuit, in North America BRI is relatively uncommon whilst PRI circuits serving PBXs are commonplace.

Bearer channel

The bearer channel (B) is a standard 64 kbit/s voice channel of 8 bits sampled at 8 kHz with G.711 encoding. B-channels can also be used to carry data, since they are nothing more than digital channels.

Each one of these channels is known as a DS0.

Most B channels can carry a 64 kbit/s signal, but some were limited to 56K because they traveled over RBS lines. This was commonplace in the 20th century, but has since become less so.

X.25

X.25 can be carried over the B or D channels of a BRI line, and over the B channels of a PRI line. X.25 over the D channel is used at many point-of-sale (credit card) terminals because it eliminates the modem setup, and because it connects to the central system over a B channel, thereby eliminating the need for modems and making much better use of the central system's telephone lines.

X.25 was also part of an ISDN protocol called "Always On/Dynamic ISDN", or AO/DI. This allowed a user to have a constant multi-link PPP connection to the internet over X.25 on the D channel, and brought up one or two B channels as needed.

Frame Relay

In theory, Frame Relay can operate over the D channel of BRIs and PRIs, but it is seldom, if ever, used.

Consumer and industry perspectives

There is a second viewpoint: that of the telephone industry, where ISDN is a core technology. A telephone network can be thought of as a collection of wires strung between switching systems. The common electrical specification for the signals on these wires is T1 or E1. Between telephone company switches, the signaling is performed via SS7. Normally, a PBX is connected via a T1 with robbed bit signaling to indicate on-hook or off-hook conditions and MF and DTMF tones to encode the destination number. ISDN is much better because messages can be sent much more quickly than by trying to encode numbers as long (100 ms per digit) tone sequences. This results in faster call setup times. Also, a greater number of features are available and fraud is reduced.

In common use, ISDN is often limited to usage to Q.931 and related protocols, which are a set of signaling protocols establishing and breaking circuit-switched connections, and for advanced calling features for the user. [13] Another usage was the deployment of videoconference systems, where a direct end-to-end connection is desirable. ISDN uses the H.320 standard for audio coding and video coding,

ISDN is also used as a smart-network technology intended to add new services to the public switched telephone network (PSTN) by giving users direct access to end-to-end circuit-switched digital services and as a backup or failsafe circuit solution for critical use data circuits.

Video conferencing

One of ISDNs successful use-cases was in the videoconference field, where even small improvements in data rates are useful, but more importantly, its direct end-to-end connection offers lower latency and better reliability than packet-switched networks of the 1990s. The H.320 standard for audio coding and video coding was designed with ISDN in mind, and more specifically its 64 kbps basic data rate. including audio codecs such as G.711 (PCM) and G.728 (CELP), and discrete cosine transform (DCT) video codecs such as H.261 and H.263. [14] [15]

ISDN and broadcast industry

ISDN is used heavily by the broadcast industry as a reliable way of switching low-latency, high-quality, long-distance audio circuits. In conjunction with an appropriate codec using MPEG or various manufacturers' proprietary algorithms, an ISDN BRI can be used to send stereo bi-directional audio coded at 128 kbit/s with 20 Hz – 20 kHz audio bandwidth, although commonly the G.722 algorithm is used with a single 64 kbit/s B channel to send much lower latency mono audio at the expense of audio quality. Where very high quality audio is required multiple ISDN BRIs can be used in parallel to provide a higher bandwidth circuit switched connection. BBC Radio 3 commonly makes use of three ISDN BRIs to carry 320 kbit/s audio stream for live outside broadcasts. ISDN BRI services are used to link remote studios, sports grounds and outside broadcasts into the main broadcast studio. ISDN via satellite is used by field reporters around the world. It is also common to use ISDN for the return audio links to remote satellite broadcast vehicles.

In many countries, such as the UK and Australia, ISDN has displaced the older technology of equalised analogue landlines, with these circuits being phased out by telecommunications providers. Use of IP-based streaming codecs such as Comrex ACCESS and ipDTL is becoming more widespread in the broadcast sector, using broadband internet to connect remote studios. [16]

Global usage

United States and Canada

ISDN-BRI never gained popularity as a general use telephone access technology in Canada and the US, and remains a niche product. The service was seen as "a solution in search of a problem", [17] and the extensive array of options and features were difficult for customers to understand and use. ISDN has long been known by derogatory backronyms highlighting these issues, such as It Still Does Nothing, Innovations Subscribers Don't Need, and IStill Don't kNow, [18] [19] or, from the supposed standpoint of telephone companies, ISmell Dollars Now. [20]

Once the term "broadband Internet access" came to be associated with data rates incoming to the customer at 256 kbit/s or more, [lower-alpha 2] and alternatives like ADSL grew in popularity, the consumer market for BRI did not develop. Its only remaining advantage is that, while ADSL has a functional distance limitation and can use ADSL loop extenders, BRI has a greater limit and can use repeaters. As such, BRI may be acceptable for customers who are too remote for ADSL. Widespread use of BRI is further stymied by some small North American CLECs such as CenturyTel having given up on it and not providing Internet access using it. [24] However, AT&T in most states (especially the former SBC/SWB territory) will still install an ISDN BRI line anywhere a normal analog line can be placed and the monthly charge is roughly $55.[ citation needed ]

ISDN-BRI is currently primarily used in industries with specialized and very specific needs. High-end videoconferencing hardware can bond up to 8 B-channels together (using a BRI circuit for every 2 channels) to provide digital, circuit-switched video connections to almost anywhere in the world. This is very expensive, and is being replaced by IP-based conferencing, but where cost concern is less of an issue than predictable quality and where a QoS-enabled IP does not exist, BRI is the preferred choice.

Most modern non-VoIP PBXs use ISDN-PRI circuits. These are connected via T1 lines with the central office switch, replacing older analog two-way and direct inward dialing (DID) trunks. PRI is capable of delivering Calling Line Identification (CLID) in both directions so that the telephone number of an extension, rather than a company's main number, can be sent. It is still commonly used in recording studios and some radio programs, when a voice-over actor or host is in one studio (possibly telecommuting from home), but the director and producer are in a studio at another location. [8] The ISDN protocol delivers channelized, not-over-the-Internet service, powerful call setup and routing features, faster setup and tear down, superior audio fidelity as compared to POTS (plain old telephone service), lower delay and, at higher densities, lower cost.

In 2013, Verizon announced it would no longer take orders for ISDN service in the Northeastern United States. [8]

Norway

On April 19, 1988, Norwegian telecommunications company Telenor began offering nationwide ISDN services trademarked INS Net 64, and INS Net 1500, a fruition of NTT's independent research and trial from the 1970s of what it referred to the INS (Information Network System). [25]

Australia

Telstra provides the business customer with the ISDN services. There are five types of ISDN services which are ISDN2, ISDN2 Enhanced, ISDN10, ISDN20 and ISDN30. Telstra changed the minimum monthly charge for voice and data calls. In general, there are two group of ISDN service types; The Basic Rate services – ISDN 2 or ISDN 2 Enhanced. Another group of types are the Primary Rate services, ISDN 10/20/30. [26] Telstra announced that the new sales of ISDN product would be unavailable as of 31 January 2018. The final exit date of ISDN service and migration to the new service would be confirmed by 2022. [27]

India

Bharat Sanchar Nigam Limited, Reliance Communications and Bharti Airtel are the largest communication service providers, and offer both ISDN BRI and PRI services across the country. Reliance Communications and Bharti Airtel uses the DLC technology for providing these services. With the introduction of broadband technology, the load on bandwidth is being absorbed by ADSL. ISDN continues to be an important backup network for point-to-point leased line customers such as banks, Eseva Centers, [28] Life Insurance Corporation of India, and SBI ATMs.

Japan

On April 19, 1988, Japanese telecommunications company NTT began offering nationwide ISDN services trademarked INS Net 64, and INS Net 1500, a fruition of NTT's independent research and trial from the 1970s of what it referred to the INS (Information Network System). [29]

Previously, in April 1985, Japanese digital telephone exchange hardware made by Fujitsu was used to experimentally deploy the world's first I interface ISDN. The I interface, unlike the older and incompatible Y interface, is what modern ISDN services use today.

Since 2000, NTT's ISDN offering have been known as FLET's ISDN, incorporating the "FLET's" brand that NTT uses for all of its ISP offerings.

In Japan, the number of ISDN subscribers dwindled as alternative technologies such as ADSL, cable Internet access, and fiber to the home gained greater popularity. On November 2, 2010, NTT announced plans to migrate their backend from PSTN to the IP network from around 2020 to around 2025. For this migration, ISDN services will be retired, and fiber optic services are recommended as an alternative. [30]

United Kingdom

In the United Kingdom, British Telecom (BT) provides ISDN2e (BRI) as well as ISDN30 (PRI). Until April 2006, they also offered services named Home Highway and Business Highway, which were BRI ISDN-based services that offered integrated analogue connectivity as well as ISDN. Later versions of the Highway products also included built-in USB sockets for direct computer access. Home Highway was bought by many home users, usually for Internet connection, although not as fast as ADSL, because it was available before ADSL and in places where ADSL does not reach.

In early 2015, BT announced their intention to retire the UK's ISDN infrastructure by 2025.[ citation needed ]

France

France Telecom offers ISDN services under their product name Numeris (2 B+D), of which a professional Duo and home Itoo version is available. ISDN is generally known as RNIS in France and has widespread availability. The introduction of ADSL is reducing ISDN use[ when? ] for data transfer and Internet access, although it is still common in more rural and outlying areas, and for applications such as business voice and point-of-sale terminals.

Germany

German stamp DBP 1988 1368 ISDN.jpg
German stamp

In Germany, ISDN was very popular with an installed base of 25 million channels (29% of all subscriber lines in Germany as of 2003 and 20% of all ISDN channels worldwide). Due to the success of ISDN, the number of installed analog lines was decreasing. Deutsche Telekom (DTAG) offered both BRI and PRI. Competing phone companies often offered ISDN only and no analog lines. However, these operators generally offered free hardware that also allows the use of POTS equipment, such as NTBAs [lower-alpha 3] with integrated terminal adapters. Because of the widespread availability of ADSL services, ISDN was primarily used for voice and fax traffic.

Until 2007 ISDN (BRI) and ADSL/VDSL were often bundled on the same line, mainly because the combination of DSL with an analog line had no cost advantage over a combined ISDN-DSL line. This practice turned into an issue for the operators when vendors of ISDN technology stopped manufacturing it and spare parts became hard to come by. Since then phone companies started introducing cheaper xDSL-only products using VoIP for telephony, [32] also in an effort to reduce their costs by operating separate data & voice networks.

Since approximately 2010, most German operators are offering more and more VoIP on top of DSL lines and ceased offering ISDN lines. As from 2018 on, new ISDN lines are not available anymore in Germany, existing ISDN lines are phased out from 2016 onwards and existing customers are encouraged to move to DSL-based VoIP products. Deutsche Telekom expected to complete this phase-out by 2018 [33] but postponed the date to 2020, other providers like Vodafone estimate to have their phase-out completed by 2022.

Greece

OTE, the incumbent telecommunications operator, offers ISDN BRI (BRA) services in Greece. Following the launch of ADSL in 2003, the importance of ISDN for data transfer began to decrease and is today limited to niche business applications with point-to-point requirements.

International deployment

A study [34] of the German Department of Science shows the following spread of ISDN-channels per 1,000 inhabitants in the year 2005:

Configurations

In ISDN, there are two types of channels, B (for "bearer") and D (for "data"). B channels are used for data (which may include voice), and D channels are intended for signaling and control (but can also be used for data).

There are two ISDN implementations. Basic Rate Interface (BRI), also called basic rate access (BRA) — consists of two B channels, each with bandwidth of 64 kbit/s, and one D channel with a bandwidth of 16 kbit/s. Together these three channels can be designated as 2B+D. Primary Rate Interface (PRI), also called primary rate access (PRA) in Europe — contains a greater number of B channels and a D channel with a bandwidth of 64 kbit/s. The number of B channels for PRI varies according to the nation: in North America and Japan it is 23B+1D, with an aggregate bit rate of 1.544 Mbit/s (T1); in Europe, India and Australia it is 30B+2D, with an aggregate bit rate of 2.048 Mbit/s (E1). Broadband Integrated Services Digital Network (BISDN) is another ISDN implementation and it is able to manage different types of services at the same time. It is primarily used within network backbones and employs ATM.

Another alternative ISDN configuration can be used in which the B channels of an ISDN BRI line are bonded to provide a total duplex bandwidth of 128 kbit/s. This precludes use of the line for voice calls while the internet connection is in use. The B channels of several BRIs can be bonded, a typical use is a 384K videoconferencing channel.

Using bipolar with eight-zero substitution encoding technique, call data is transmitted over the data (B) channels, with the signaling (D) channels used for call setup and management. Once a call is set up, there is a simple 64 kbit/s synchronous bidirectional data channel (actually implemented as two simplex channels, one in each direction) between the end parties, lasting until the call is terminated. There can be as many calls as there are bearer channels, to the same or different end-points. Bearer channels may also be multiplexed into what may be considered single, higher-bandwidth channels via a process called B channel BONDING, or via use of Multi-Link PPP "bundling" or by using an H0, H11, or H12 channel on a PRI.

The D channel can also be used for sending and receiving X.25 data packets, and connection to X.25 packet network, this is specified in X.31. In practice, X.31 was only commercially implemented in the UK, France, Japan and Germany.

Reference points

A set of reference points are defined in the ISDN standard to refer to certain points between the telco and the end user ISDN equipment.

Most NT-1 devices can perform the functions of the NT2 as well, and so the S and T reference points are generally collapsed into the S/T reference point.

In North America, the NT1 device is considered customer premises equipment (CPE) and must be maintained by the customer, thus, the U interface is provided to the customer. In other locations, the NT1 device is maintained by the telco, and the S/T interface is provided to the customer. In India, service providers provide U interface and an NT1 may be supplied by Service provider as part of service offering.

Types of communications

Providing a backup line for business's inter-office and internet connectivity was a popular use of the technology [35]

Sample call

The following is an example of a Primary Rate (PRI) ISDN call showing the Q.921/LAPD and the Q.931/Network message intermixed (i.e. exactly what was exchanged on the D-channel). The call is originating from the switch where the trace was taken and goes out to some other switch, possibly an end-office LEC , who terminates the call.

The first line format is <time><D-channel><Transmitted/Received><LAPD/ISDN message ID>. If the message is an ISDN level message, then a decoding of the message is attempted showing the various Information Elements that make up the message. All ISDN messages are tagged with an ID number relative to the switch that started the call (local/remote). Following this optional decoding is a dump of the bytes of the message in <offset><hex> ... <hex><ascii> ... <ascii> format.

The RR messages at the beginning prior to the call are the keep alive messages. SETUP message indicate the start of the call. Each message is acknowledged by the other side with a RR.

10:49:47.33  21/1/24  R  RR  0000  02 01 01 a5                                          ....  10:49:47.34  21/1/24  T  RR 0000  02 01 01 b9                                          ....  10:50:17.57  21/1/24  R  RR 0000  02 01 01 a5                                          ....  10:50:17.58  21/1/24  T  RR 0000  02 01 01 b9                                          ....  10:50:24.37  21/1/24  T  SETUP     Call Reference       : 000062-local     Bearer Capability    : CCITT, Speech, Circuit mode, 64 kbit/s     Channel ID           : Implicit Interface ID implies current span, 21/1/5, Exclusive     Calling Party Number : 8018023000 National number  User-provided, not screened  Presentation allowed     Called Party Number  : 3739120 Type: SUBSCRB 0000  00 01 a4 b8  08 02 00 3e  05 04 03 80  90 a2 18 03   .......>........ 0010  a9 83 85 6c  0c 21 80 38  30 31 38 30  32 33 30 30   ...l.!.801802300 0020  30 70 08 c1  33 37 33 39  31 32 30                   0p..3739120  10:50:24.37  21/1/24  R  RR 0000  00 01 01 a6                                          ....  10:50:24.77  21/1/24  R  CALL PROCEEDING     Call Reference       : 000062-local     Channel ID           : Implicit Interface ID implies current span, 21/1/5, Exclusive 0000  02 01 b8 a6  08 02 80 3e  02 18 03 a9  83 85         .......>......  10:50:24.77  21/1/24  T  RR 0000  02 01 01 ba                                          ....  10:50:25.02  21/1/24  R  ALERTING     Call Reference       : 000062-local     Progress Indicator   : CCITT, Public network serving local user, In-band information or an appropriate pattern is now available 0000  02 01 ba a6  08 02 80 3e  01 1e 02 82  88            .......>.....  10:50:25.02  21/1/24  T  RR 0000  02 01 01 bc                                          ....  10:50:28.43  21/1/24  R  CONNECT     Call Reference       : 000062-local 0000  02 01 bc a6  08 02 80 3e  07                         .......>.  10:50:28.43  21/1/24  T  RR 0000  02 01 01 be                                          ....  10:50:28.43  21/1/24  T  CONNECT_ACK     Call Reference       : 000062-local 0000  00 01 a6 be  08 02 00 3e  0f                         .......>.  10:50:28.44  21/1/24  R  RR 0000  00 01 01 a8                                          ....  10:50:35.69  21/1/24  T  DISCONNECT     Call Reference       : 000062-local     Cause                : 16, Normal call clearing. 0000  00 01 a8 be  08 02 00 3e  45 08 02 8a  90            .......>E....  10:50:35.70  21/1/24  R  RR 0000  00 01 01 aa                                          ....  10:50:36.98  21/1/24  R  RELEASE     Call Reference       : 000062-local 0000  02 01 be aa  08 02 80 3e  4d                         .......>M  10:50:36.98  21/1/24  T  RR 0000  02 01 01 c0                                          ....  10:50:36.99  21/1/24  T  RELEASE COMPLETE     Call Reference       : 000062-local 0000  00 01 aa c0  08 02 00 3e  5a                         .......>Z  10:50:36.00  21/1/24  R  RR 0000  00 01 01 ac                                          ....  10:51:06.10  21/1/24  R  RR 0000  02 01 01 ad                                          ....  10:51:06.10  21/1/24  T  RR 0000  02 01 01 c1                                          ....  10:51:36.37  21/1/24  R  RR 0000  02 01 01 ad                                          ....  10:51:36.37  21/1/24  T  RR 0000  02 01 01 c1                                          .... 

See also

Protocols


Specifications defining the physical layer and part of the data link layers of ISDN:

Other

Notes

  1. His boss told him to "sit down and shut up." [3]
  2. Broadband Internet access: Although various minimum bandwidths have been used in definitions of broadband, ranging up from 64 kbit/s up to 1.0 Mbit/s, the 2006 OECD report [21] is typical by defining broadband as having download data transfer rates equal to or faster than 256 kbit/s, while the United States FCC, as of 2008, defines broadband as anything above 768 kbit/s. [22] [23] The trend is to raise the threshold of the broadband definition as the marketplace rolls out faster services. [23]
  3. "Network Termination for ISDN Basic Access", little boxes that bridge the two-wire UK0 line to the four-wire S0 bus. [31]

Related Research Articles

Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access.

The Primary Rate Interface (PRI) is a telecommunications interface standard used on an Integrated Services Digital Network (ISDN) for carrying multiple DS0 voice and data transmissions between the network and a user.

Telephony is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is intimately linked to the invention and development of the telephone.

The U interface or U reference point is a Basic Rate Interface (BRI) in the local loop of an Integrated Services Digital Network (ISDN). It is characterized by the use of a 2-wire transmission system that connects the network termination type 1 (NT1) on the customer's premises and the line termination (LT) in the carrier's local exchange. It is not as distance sensitive as a service using an S interface or T interface.

Basic Rate Interface

Basic Rate Interface or Basic Rate Access is an Integrated Services Digital Network (ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for voice-grade telephone service. As such, an ISDN BRI connection can use the existing telephone infrastructure at a business.

Digital subscriber line access multiplexer Network equipment

A digital subscriber line access multiplexer is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital communications channel using multiplexing techniques.

ISDN Digital Subscriber Line (IDSL) uses ISDN-based digital subscriber line technology to provide a data communication channel across existing copper telephone lines at a rate of 144 kbit/s, slightly higher than a bonded dual channel ISDN connection at 128kbit/s. The digital transmission bypasses the telephone company's central office equipment that handles analogue signals. IDSL uses the ISDN grade loop without Basic Rate Interface in ISDN transmission mode. The benefits of IDSL over ISDN are that IDSL provides always-on connections and transmits data via a data network rather than the carrier's voice network.

Internet access Individual connection to the internet

Internet access is the ability of individuals and organizations to connect to the Internet using computer terminals, computers, and other devices; and to access services such as email and the World Wide Web. Internet access is sold by Internet service providers (ISPs) delivering connectivity at a wide range of data transfer rates via various networking technologies. Many organizations, including a growing number of municipal entities, also provide cost-free wireless access and landlines.

The public switched telephone network (PSTN) is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telephony operators, providing infrastructure and services for public telecommunication. The PSTN consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all interconnected by switching centers, thus allowing most telephones to communicate with each other. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital in its core network and includes mobile and other networks, as well as fixed telephones.

A leased line is a private telecommunications circuit between two or more locations provided according to a commercial contract. It is sometimes also known as a private circuit, and as a data line in the UK. Typically, leased lines are used by businesses to connect geographically distant offices.

Single-pair high-speed digital subscriber line (SHDSL) is a form of symmetric digital subscriber line (SDSL), a data communications technology for equal transmit and receive data rate over copper telephone lines, faster than a conventional voiceband modem can provide. As opposed to other DSL technologies, SHDSL employs trellis-coded pulse-amplitude modulation (TC-PAM). As a baseband transmission scheme, TC-PAM operates at frequencies that include those used by the analog voice plain old telephone service (POTS). As such, a frequency splitter, or DSL filter, cannot be used to allow a telephone line to be shared by both an SHDSL service and a POTS service at the same time. Support of symmetric data rates made SHDSL a popular choice by businesses for private branch exchange (PBX), virtual private network (VPN), web hosting and other data services.

Digital Signal 1 is a T-carrier signaling scheme devised by Bell Labs. DS1 is the primary digital telephone standard used in the United States, Canada and Japan and is able to transmit up to 24 multiplexed voice and data calls over telephone lines. E-carrier is used in place of T-carrier outside the United States, Canada, Japan, and South Korea. DS1 is the logical bit pattern used over a physical T1 line; in practice, the terms "DS1" and "T1" are often used interchangeably.

ANSI T1.413 is a technical standard that defines the requirements for the single asymmetric digital subscriber line (ADSL) for the interface between the telecommunications network and the customer installation in terms of their interaction and electrical characteristics. ADSL allows the provision of voiceband services including plain old telephone service (POTS) and data services up to 56 kbit/s, and a variety of digital channels. In the direction from the network to the customer premises (downstream), the digital bearer channels may consist of full-duplex low-speed bearer channels and simpler high-speed bearer channels; in the other (upstream) direction, only low-speed bearer channels are provided.

Digital access carrier system

Digital access carrier system (DACS) is the name used by British Telecom in the United Kingdom for a 0+2 pair gain system.

DSL modem Type of computer network modem; network equipment

A digital subscriber line (DSL) modem is a device used to connect a computer or router to a telephone line which provides the digital subscriber line service for connection to the Internet, which is often called DSL broadband.

The BT Versatility is a telephone PBX switchboard sold by BT and targeted at small businesses. It is manufactured by Taratel Communications previously Lake Communications in Ireland as the OfficeLink. In South Africa it was sold by Tellumat as the Convergence 30 or C30, in Australia it was sold as the Commander Connect, in the USA it was sold by Inter-tel as the Encore CX and by Mitel as the Mitel 3000

High-bit-rate digital subscriber line (HDSL) is a telecommunications protocol standardized in 1994. It was the first digital subscriber line (DSL) technology to use a higher frequency spectrum over copper, twisted pair cables. HDSL was developed to transport DS1 services at 1.544 Mbit/s and 2.048 Mbit/s over telephone local loops without a need for repeaters. Successor technology to HDSL includes HDSL2 and HDSL4, proprietary SDSL, and G.SHDSL.

The prevalent means of connecting to the Internet in Germany is DSL, introduced by Deutsche Telekom in 1999. Other technologies such as Cable, FTTH and FTTB (fiber), Satellite, UMTS/HSDPA (mobile) and LTE are available as alternatives.

BT Highway was a UK retail ISDN2e service from British Telecom which was announced in November 1997 and withdrawn in February 2007. In the domestic market, it was sold as BT Home Highway and for small businesses, BT Business Highway. These names were used simply to differentiate billing schemes; the hardware for both services used the name BT Highway. Unlike regular ISDN2e service where only a digital S interface is provided BT Highway provided both digital and analogue connections simplifying migration from regular POTS service.

References

Citations

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  3. 1 2 3 4 5 6 Cioffi 2011, p. 31.
  4. 1 2 Cioffi 2011, p. 32.
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  24. "Disclaimer", Internet Access service offerings, CenturyTel, You may not obtain Internet services over ISDN lines (BRI or PRI), dedicated circuits or special service circuits.
  25. "NTT東日本 - 北浜ビル" (in Norwegian). NO: Kajo.|contribution= ignored (help)
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  30. "PTSNのマイグレーションについて~概括的展望~" (PDF) (in Japanese). JP: NTT East. November 2, 2010. Archived from the original (PDF) on April 21, 2012. Retrieved June 20, 2014.
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  32. Neuhetzki, Thorsten (24 Jan 2007). "Arcor will ab Sommer Fernsehen per Internet anbieten". teltarif.de. Retrieved 7 May 2016. Arcor setzt im Endkundenbereich auf NGN
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Bibliography